Influence of electron cyclotron current drive on the transition between normal sawteeth and the stationary state

Abstract

The transition between normal sawteeth and a sawtooth-free stationary state after electron cyclotron current drive (ECCD) deposition has been numerically investigated by the CLT code. The periods of normal sawteeth decrease if co-ECCD deposits inside the initial q=1 surface and increase when co-ECCD deposits outside the q=1 surface. When co-ECCD deposits in the vicinity of the q=1 surface, the normal sawteeth can be converted into a stationary state, during which sawteeth are completely prevented. The stationary state can also be converted into normal sawteeth if co-ECCD is injected just outside the q=1 surface. The mechanism of the transition between normal sawteeth and sawtooth-free stationary states is then discussed.